1. Field of the Invention
The invention relates generally to the control of emissions from associated gas. More particularly, the invention relates to energy generation and the control of emissions from associated gas by the use of microturbines adapted to utilize both high-heating-value gas and low-heating-value gas.
2. Background of the Invention
Hydrocarbon gases are almost always associated with crude oil in an oil reserve, as they represent the lighter chemical fraction (shorter molecular chain) formed when organic remains are converted into hydrocarbons. Such hydrocarbon gases may exist separately from the crude oil in the underground formation or be dissolved in the crude oil. As the crude oil is raised from the reservoir to the surface, pressure is reduced to atmospheric, and the dissolved hydrocarbon gases come out of solution. Such gases occurring in combination with produced crude oil are often referred to as “associated” or “casinghead” gas.
Although associated gas contains energy in the form of combustible hydrocarbons, it is typically not utilized because facility upgrade costs necessary to convert the energy into a usable form and distribution costs limit economic recovery. Consequently, in many production operations, the associated gas is treated as a by-product or waste product of oil production and is typically disposed of via venting or flaring to the environment.
Venting and flaring are relatively inexpensive ways to deal with associated gas, but result in relatively high emissions (e.g., large quantities of greenhouse gases) and fail to capture any of the energy contained within the associated gas. Improved flaring systems and methods have been developed to reduce flare emissions sufficiently to satisfy stringent emission standards, however, many of these improved flaring systems merely convert the energy within the associated gas into thermal energy that is passed to the environment and do not leverage the energy contained within the associated gas.
In some production operations, combustion generators are employed to consume associated gases and produce power (e.g., electrical power, mechanical power, etc.). Such approaches improve conversion efficiency and lower emissions but depend, at least in part, on the associated gas properties (e.g., pressure, composition, specific energy density, etc.). In particular, the associated gas properties must meet the operational parameters and specifications of the combustion generator. For instance, many combustion generators designed for hydrocarbon gases operate effectively with gases having a specific energy density between 350 Btu/scf and 1700 Btu/scf. If the hydrocarbon gas fueling the combustion generator has a specific energy density outside this operational range, the combustion generator may operate inefficiently or not at all. Since associated gas makeup within a well and across different wells can vary greatly, the usefulness of such combustion generator systems also varies.
Accordingly, there remains a need in the art for methods and systems to reduce oil production operation emissions resulting from associated gas while converting the energy contained in the associated gas into a more useful form (e.g., electrical or mechanical power). Such systems and methods would be particularly well received if they were designed and configured to accommodate associated gas of varying makeup and could be effectively utilized with associated gas having a specific energy density outside the operating range of conventional combustion generators.